Upon exposure to abiotic stresses such as drought, high salinity, low temperature and etc., plant will not simply passively endure the stressful conditions. In stead, plant will actively cope with the environmental stresses through eliciting responses of its in-built defense system, including, e.g., biosynthesis of new proteins, changes in metabolism, accumulation of stress-tolerant chemicals, and so on (Hans J. Plant cell. 1995, 7: 1099-1111). Many proteins are involved in plant response to abiotic stresses (Ashwani Pareek. Current Science. 1998, 75: 1170-1174) and they act coordinatively to enhance tolerance by modulating biochemical, metabolic and physiological adaptions. Studies have shown that enhancing the expression of single effector protein genes was not able to significantly improve plant performance under stress conditions.
Under abiotic stress conditions, many proteins induced in plant are involved in tolerance to abiotic stresses. The genes encoding some of the proteins have been cloned (Anil Grover. Current Science. 1998, 75: 689-695). In efforts to increase plant tolerance to abiotic stresses, such as cold, drought and salt, many stress-related genes from various sources have been cloned and transformed into different plant species (Shavindra Bajaj. Molecular Breeding. 1999, 5: 493-503). The proteins encoded by those cloned genes can be classified into three groups: 1) Enzymes involved in the synthesis of osmolyte. For example, the introduction of gene mtlD derived from E. coli into tobacco increased the content of mannitol in the crop. Transgenic tobacco or rice over-expressing P5CS gene elevated its content of proline. The introduction of codA gene into arabidopsis or rice increased the content of glycine betaine in transgenic plants (Sakamoto A. PMB. 1998, 38: 1011-1019). 2) Late Embryogenesis Abundant (LEA) and related proteins. For example, constitutive expression of cor15a gene in arabidopsis discouraged the formation of freeze-induced harmful membrane structures (Steponkus PL. PNAS. 1998, 95: 14570-14575). 3) Proteins related to oxidative stress. For example, over-expressing of Mn-SOD gene in alfalfa (Mckersic BD. Plant Physiol. 1996, 111: 1177-1181) and of GST gene in tobacco increased tolerance to stresses. However, although the expression of single effector genes in transgenic plants can enhance an aspect of plant stress responses under experimental conditions, the overall performance of the transgenic plants under stresses was not largely improved. Recently, the gene encoding an tolerance-related transcription factor CBF1 (C-repeat Binding Factor) was over-expressed in arabidopsis and showed that CBF1 enhanced the expression of a series of cold-related effector genes. Moreover, Compared with the above described plants over-expressing single effector genes, the enhanced expression of CBF1 significantly improved the cold tolerance in transgenic arabidopsis plants (Kirsten R. Science. 1998, 280: 104-106). Similarly, over expression of transcription factor DREB1A gene in arabidopsis induced multiple stress-related genes and largely increased plant tolerance to salt, cold and drought stresses (Mie Kasuga. Nature Biotechnology. 1999, 17: 287-291).
Studies show that plants produce a large amount of reactive oxygen species (ROS) under stress conditions such as drought, salinity and low temperature, leading to oxidative stress. (Zhu J K. Trends Plant Sci. 2001, 6: 66-71). Because ROS are highly active, they can lead to serious damages to cells, for example, membrane peroxidation, inactivation of key enzymes, DNA lesions and etc. Therefore, the scavenging of excess ROS is critical for plants to increase tolerance to abiotic stresses. Catalase (e.g., CAT1) plays an important role in the scavenging of ROS. However, under stress conditions, the plant's ability for induction of its endogenous anti-oxidant system is poor, which limits the further increase of plant tolerance. Therefore, the cloning of genes encoding the transcription factors that regulate the expression of Cat1 will not only further our understanding on ROS signal tranduction pathway, but provide strategies for generating new crop varieties with enhanced tolerance to stresses such as drought, salt, cold and etc. This is because such trans-acting factor can regulate the expression of anti-oxidant genes including Cat1, as well as other stress-responsive genes.
ABRE is an ABA (abscisic acid) responsive element located in the promoter region of many stress responsive genes, which is characterized by (C/G/T)ACGTG(G/T)(A/C) (SEQ ID NO: 31 sequence (Chen WQ. Plant Cell. 2001, 14: 559-574). The promoter region of Cat1 contains two ABRE-like DNA sequence, namely ABRE1 and ABRE2. Deletion analysis shows that ABRE2 (5′-GAAGTCCACGTGGAGGTGG) (SEQ ID NO: 7) is the cis-element necessary for the regulation of Cat1 by ABA. The expression of Cat1 increases along with the elevation of ABA content during maize embryogenesis, a process in which seeds accumulate nutrients and undergo deccicated as well as induction of tolerance to dehydration. Previous study showed that there existed trans-acting factors interacting with ABRE2 in cells during maize embrogenesis. The trans-acting factors can be classified into two groups, one is ABA-dependent (namely Cat1 promoter Binding Factor 1, CBF1), and the other is ABA-independent (namely Cat1 promoter Binding Factor 2, CBF2) (Lingqing M. Guan, The Plant Journal. 2000, 22(2): 87-95). These transcription factors have not been cloned up to now.